Dense to columnar microstructure evolution of Ba(Mg1/3Ta2/3)O3 TBCs through tailoring of suspension plasma spray conditions

Inductively-coupled plasma spraying was used to deposit Ba(Mg1/3Ta2/3)O3 (BMT) thermal barrier coatings on a titanium alloy substrate. By selecting the appropriate atomization probe and adjusting both the precursor feed rate and spraying distance, it was possible to tune the BMT coating microstructure from dense splat-like layers to columns. Of those parameters, the spraying distance was the most crucial parameter to form a columnar microstructure. An atomization probe that fed a bimodal distribution of droplet size was considered as an important prerequisite to obtain a high-quality columnar structure. This is further discussed as part of the column formation mechanism. The effect of substrate surface roughness was studied separately. The combination of a finely sand-blasted substrate and a precursor feed rate of 8 ml/min led to the desired columnar structure with an intracolumnar porosity of 4.3 % and an intercolumnar porosity 10 %. The deposition rate achieved is suitable for industrial application.